1. Field to Which the Invention Pertains
Well known to physicians is the fact that individuals may, for a variety of reasons, lose control of their urinary function. Although the reasons for the loss of urinary control are manifold, the consequent treatment is a rather well accepted medical practice which involves inserting a tube or catheter up the urinary passage until the remote or distal end is located within the bladder. The near or proximal end of the catheter remains outside of the body and there is thus provided a path or means through which the bladder may drain. Once a catheter has been passed through the urinary tract and inserted into the bladder, it is generally medically desirable to have the catheter retained in the urinary tract with the distal end of the catheter positioned within the bladder. Catheters which are designed for such a function are called urinary retention catheters and are generally provided with some means to promote retention. Typically, this retention capability is provided by including an inflatable balloon at the distal end of the catheter. During insertion, the balloon is deflated. After the distal end of the catheter is positioned within the bladder, the balloon is inflated by passing a fluid, typically water, through a passage within the catheter which is referred to as an inflation lumen. When the balloon is inflated, the inflation lumen is sealed and the inflated balloon within the bladder insures retention. Thereafter, the bladder may drain through a second passage within the catheter, i.e. the drainage lumen.
There are a number of medical procedures which involve the use of catheters and, as a result, catheters are generally referred to by a name associated with their function, e.g. urinary catheters, tracheal catheters, venous catheters, etc. While all such catheters must be fabricated so as to insure the safety and comfort of the patient, the physiological demands imposed upon a urinary retention catheter are particularly severe and appear to result in conflicting design criteria. For example, the comfort of the patient dictates that a urinary retention catheter be as soft and as flexible as possible. On the other hand, from a structural point of view, such a catheter must be sufficiently rigid to insure that as it traverses the urinary tract, the catheter tube will not bend to an extent which results in occluding or reducing the size of the drainage lumen and the inflation lumen. Similarly, it is clearly desirable that the outer diameter of the catheter be as small as possible while the diameter of the drainage lumen be as large as possible. However, the maximum outer diameter of the catheter is substantially defined by the diameter of the urinary tract and the comfort of the patient while the contractive forces which are exerted on the catheter by the urinary tract substantially define a minimum wall thickness between the drainage lumen and the exterior of the catheter.
Of substantial concern to both the patient and the physician is the balloon and its proper inflation. After the catheter is inserted, it is desirable that the balloon be so constructed and arranged that it can be inflated with a minimum inflation pressure. Such an objective is desirable because the maximum inflation pressure required to inflate a balloon will be the determining factor with respect to the minimum wall thickness surrounding the inflation lumen. Since one desires to maximize the size of the drainage lumen and since the area occupied by the inflation lumen diminishes the size of the drainage lumen, it follows that one wishes to utilize a minimum wall thickness for the inflation lumen and, therefore, the balloon construction should be such as to require a minimum pressure for inflation. While one may construct a urinary retention catheter having a balloon which will inflate with a minimum pressure, the resulting structure may, and often does, possess undesirable features. For example, to achieve a low inflation pressure, a soft and pliant material may be used for the balloon. However, from a manufacturing point of view, it is generally most economical to fabricate the balloon as an integral part of the catheter tip and, thus, the catheter tip will also be soft and pliant. Constructions of this type, which are known to the prior art, unfortunately possess certain disadvantages which are discussed hereinafter.
Finally, urinary retention catheters must not only meet or exceed the various medical and patient oriented criteria discussed above but, in addition, such a catheter must be of a construction which lends itself to a method of high volume, low cost manufacture. Such manufacturing criteria are particularly significant with respect to urinary retention catheters since tolerances are critical yet the cost of the resulting product must be consonant with the disposable nature of the product.
The invention disclosed herein relates to novel catheters and the method of manufacturing such catheters.
2. Prior Art
In an attempt to satisfy the various and conflicting criteria heretofore discussed, the prior art reflects an evolution of catheter designs. For several decades, all urinary retention catheters were manufactured by a dipping process wherein two longitudinally adjacent wires were dipped in a latex bath until a catheter tube of the desired diameter was built up. Subsequently, a hole was pierced through the wall of the tube at one end and communicated with the cavity formed by one of the two wires, which cavity would later be the inflation lumen. Thereafter, a release agent was deposited around the tube in the area of the hole and the end of the tube was again dipped to build up another layer of latex at the end of the tube and which would constitute the balloon.
The catheter which resulted from this method of manufacture was widely accepted. However, certain disadvantages of the catheter construction by this method of manufacture have been recognized. One disadvantage arises from the dipping process whereby precise dimensional control of the catheter diameter tends to be problemsome which, in turn, tends to increase the manufacturing cost.
While the strength and elasticity of latex rubber renders that material ideal as a catheter material, it has been found that, as do most materials, it poses a degree of susceptibility to encrustation from the salts commonly found in urine. On the other hand, recent developments in materials technology have made available the silicone rubbers which promise to be relatively free of susceptibility to encrustation.
Thus, more recent prior art catheter constructions have embodied silicone rubber tubes for the tip and body to relieve the encrustation problem and to enjoy a further advantage of compatibility with human tissues. Although the prior art has established that silicone rubber is an acceptable material for a catheter, the problem still remains as to the structure of the catheter and the method of manufacturing a particular structure. The problems associated with prior art silicone rubber catheter constructions is exemplified by the catheter construction disclosed by Birtwell in U.S. Pat. No. 3,547,126. The Birtwell construction employs an extruded silicone tube as the body of the catheter in combination with a molded silicone tip which is provided with a rearwardly extending portion. The rearwardly extending portion is attached to the catheter tube or body and forms the inflation balloon. The tip portion, which is abuttingly affixed to the tube or body portion, is provided with a drainage lumen that must be aligned with the drainage lumen in the body of the catheter. Because of this construction, a number of problems arise both in the manufacture of the catheter and in the use thereof. For example, as previously stated, it is desired that the pressure required to inflate a balloon should be as low as possible and thus the balloon material should be soft and relatively elastic. However, in a catheter construction of the type disclosed by Birtwell, the tip and balloon are molded as one piece and, therefore, the tip will have the same mechanical properties as the balloon. Since the tip extends longitudinally substantially beyond the end of the extruded tube and since the material used to form the tip will have a low modulus of elasticity in order to insure that the balloon is easily inflated, the tip may deflect and bend during insertion, i.e. the tip portion does not possess the required rigidity. Moreover, in the Birtwell construction any bending of the tip is especially deleterious because of the glued, butt joint connection between the tip and the body, i.e. any bending of the tip will tensionally stress the bond between the tip and the body with the probable result of a failure of the bond.
Finally, because the tip in the Birtwell construction includes a drainage lumen, assembly of the tip and the tube is exacting if a misalignment is to be avoided. The problem of avoiding a misalignment during the assembly of the tip and the tube is economically significant since the avoidance of such misalignment requires that one must resort to either a manual assembly or a sophisticated mechanical assembly.
Another manufacturing difficulty associated with catheters of the type disclosed by Birtwell relates to the problems of the bond between the tip and the tube. More particularly, since this bond is essentially a butt joint, an adhesive of extraordinary strength is required. Indeed, in practice, it has been found to be difficult to locate an adhesive which is sufficiently strong to withstand the stresses to which this joint is subjected. In addition, however, even if an adhesive of sufficient strength is employed, it has been found that when the adhesive sets the tip is often longitudinally misaligned with the tube. While the cause of the misalignment phenomenon is not clearly understood, it is believed that the problem may arise from either an uneven amount of adhesive being initially deposited on the tip or, alternatively, from an uneven drying or curing of the adhesive. In any event, the problem is manifest and is present almost to the point of precluding economic manufacture of such a construction.
The catheter construction disclosed hereinafter and the method of manufacture substantially overcomes all of the problems associated with prior art catheters and their method of manufacture.